This disclosure relates generally to diagnostic imaging and, more particularly, to improved power distribution unit for a computed tomography (CT) system.
Typically, in computed tomography (CT) imaging systems, an x-ray source emits a fan or cone-shaped beam toward a subject or object, such as a patient or a piece of luggage. Hereinafter, the terms “subject” and “object” shall include anything capable of being imaged. The beam, after being attenuated by the subject, impinges upon an array of radiation detectors. The intensity of the attenuated beam radiation received at the detector array is typically dependent upon the attenuation of the x-ray beam by the subject. Each detector element of the detector array produces a separate electrical signal indicative of the attenuated beam received by each detector element. The electrical signals are transmitted to a data processing system for analysis which ultimately produces an image.
Generally, the x-ray source and the detector array are rotated about the gantry within an imaging plane and around the subject. X-ray sources typically include x-ray tubes, which emit the x-ray beam at a focal point. X-ray detectors typically include a collimator for collimating x-ray beams received at the detector, a scintillator for converting x-rays to light energy adjacent the collimator, and photodiodes for receiving the light energy from the adjacent scintillator and producing electrical signals therefrom. Typically, each scintillator of a scintillator array converts x-rays to light energy. Each scintillator discharges light energy to a photodiode adjacent thereto. Each photodiode detects the light energy and generates a corresponding electrical signal. The outputs of the photodiodes are transmitted to the data processing system for image reconstruction. Imaging data may be obtained using x-rays that are generated at a single polychromatic energy. However, some systems may obtain multi-energy images that provide additional information for generating images.
The x-ray generator of a CT system is typically located within the gantry and, as such, rotates about an imaging bore during data acquisition on a rotatable side of the gantry. The x-ray generator includes the x-ray source, a high voltage power supply (HVPS), and an inverter that is operationally connected to a slip ring. External to the slip ring and on the stationary side of the gantry is a power distribution unit (PDU). The inverter is typically fed with a DC voltage, for example, 650 VDC, and generates an AC waveform of, for example, approximately 300 VAC, at a frequency of typically 20-50 kHz. The AC frequency is fed to the HV tank, which has a transformer and rectifiers that develop a DC HV potential. The HV potential is applied to the x-ray source.
According to one known configuration, a typical PDU used in an imaging application such as CT includes a large and relatively expensive transformer that operates at line frequency, such as 50 or 60 Hz. Multiple secondary windings generate unregulated DC voltage for X-ray generation, and generate AC power to the rest of the system. A large capacitor, between the PDU and the x-ray inverter, is used to minimize voltage droop, and as a result mechanical contactors are included to limit inrush current due to the large capacitor. The mechanical contactors can cause reliability problems over time. In addition, the large transformer typically remains energized even when the CT system is not in use, consuming in some known systems 500 W or more.
Therefore, it would be desirable to have an improved power distribution unit for a CT system.